The invention relates to hydraulically actuated telescoping booms, where a hydraulic piston is used to extend or retract an external object, particularly as found on heavy construction machinery, and more particularly to method and apparatus for detecting the position of the boom.
In the heavy construction industry, especially in the mobile crane industry, it is necessary to know the position of hydraulically actuated moving parts, e.g. booms, which extend from machines, e.g. cranes, in order to avoid serious accidents. Thus, sensors or measuring devices are installed on the equipment to measure the boom length on telescoping booms, as well as boom angles, extension distances on outriggers, and the travel distances to foot pads located on outriggers.
In the case of telescoping booms, a device called a xe2x80x9ccable reelxe2x80x9d is installed to measure boom extension distances. The cable reel device consists of a circular wrapped coil of wire which is slowly pulled out of a circular reel when the boom is telescoped out. The distance of the boom travel is measured as a function of the number of revolutions of the cable reel.
A major problem with this conventional approach to measuring boom travel or distance is due to the external position of the measuring device, e.g. cable reel. Because it is mounted on the outside of the boom, it becomes subject to the environmental influence of wind, rain, mud, dirt, and shock, and often comes in contact with tree branches and other objects located within the construction area. As a direct result of these environmental factors, and in combination with the control actions of the equipment operator, the reliability of the cable reel is relatively low, more than one failure per 3050 hours of operation.
Therefore it is desirable to more reliably measure the distance of travel of a hydraulically actuated boom telescoping out or in from a crane or similar equipment, including but not limited to bucket loaders, dump trucks, grade levelers, aerial work platforms, tractors, combines, and bulldozers.
Accordingly it is an object of the invention to provide a method and apparatus for reliably measuring the distance of travel of a hydraulically actuated telescoping boom.
It is another object of the invention to provide a detection system for measuring the distance of travel of a hydraulically actuated telescoping boom which is better and more reliable than a cable reel system.
The invention is a method and apparatus for reliably measuring the distance of travel of a hydraulically actuated telescoping boom by measuring the flow rate of the hydraulic fluid used to actuate the boom. By measuring the flow rate of hydraulic fluid into or out of a fixed diameter hydraulic cylinder, and integrating under this fluid flow function over a period of time, the volume of hydraulic fluid which has been transferred into or out of the hydraulic cylinder in that period of time is mathematically determined. Once the volume of fluid is known in a fixed size hydraulic cylinder, the distance of piston travel is easily determined. Once the location of the piston is determined within the hydraulic cylinder, the boom length, or the length of any stroke distance, is determined because they are linearly correlated with an r value (Pearson Correlation Coefficient) approaching 1.0. Thus, boom position is determined from knowledge of piston location within the cylinder, which is determined from simple measurement of hydraulic fluid flow rate.
To implement the invention, a flow meter is placed at the input, e.g. in an input line or in the intake manifold, of the hydraulic cylinder, and another flow meter, preferably of the same type and make, is placed at the outlet, e.g. in an outlet line or in the exhaust manifold, of the cylinder. While a single flow meter at either the input or output may be used, the use of two flow meters, one at the intake and one at the exhaust of the hydraulic cylinder, greatly increases reliability. The signals from the flow meters (or single flow meter) are input into a processor which calculates the boom position. Zero calibration is automatically nulled using a microswitch when the piston reaches its minimum or maximum position in the cylinder. If a vertical piston is also used to push a boom up and down about a pivot point, then the system can be used to determine boom angle as well as boom extension.
The invention is applicable to hydraulically actuated booms and similar extendable elements which are extended from or retracted into a hydraulic cylinder by a hydraulic piston. In particular, the invention can be used for heavy construction machinery.